This invention relates to radioactive decontamination methods and more particularly to flow control methods for radioactively decontaminating nuclear steam generators.
A major problem encountered in performing maintenance on nuclear power plant equipment is the radiation exposure of maintenance personnel. Since the coolant that circulates through the nuclear reactor system is exposed to radiation, the coolant carries the radioactivity through most of the components of the nuclear reactor system. This circulation of the coolant through the nuclear reactor system causes many of the components of the nuclear reactor to become radioactive. Occasionally, over the life of the nuclear power plant, certain of the components of the nuclear power plant system need to have maintenance performed on them. When it is necessary to perform maintenance on these components, it is sometimes necessary for maintenance personnel to come in close contact with these components. Since the components are radioactive, care must be taken by the working personnel to avoid overexposure from this radiation. When the operations to be performed on these components requires a great deal of time, the radiation field associated with the contaminated components poses great difficulty in performing these operations because of the limited time in which any particular working personnel may be allowed to be present near the component. Under certain circumstances the radiation field of the component may greatly extend the time to perform the maintenance and it may also greatly increase the number of working personnel needed to perform the task because each of the personnel may only be present near the component for a limited amount of time. Therefore, it has become necessary to develop techniques for reducing the radiation field associated with these components so that working personnel may be present near the components for a greater length of time so as to be able to perform the maintenance procedures in an expedient manner.
It has been known that the radiation field associated with these components is produced by the radio-activity deposited in the thin oxide film that has become deposited on the inside surfaces of these components. Methods for reducing the radioactive field associated with these components have centered on removing the radioactive metal oxide film without damaging the component. Methods which have been tried to remove this metal oxide film include grit blasting, rinsing the components with solutions, and wiping of the surface. Difficulties which arise with some of these methods include the inability to easily clean the rough surface of some types of components, the airborne radiation caused by removing the oxide film such as in grit blasting, and possible contamination of the primary or secondary side cooling water by residual materials from these methods. Therefore, what is needed is a method for radioactively decontaminating components of nuclear power plants so that maintenance may be performed thereon without damaging the component or spreading the contaminates throughout the reactor system.